Thanks a lot Mr. Breen for your post, that's why I always keep comming back to read this forum.
Even I'm a young engineer, I've seen many mistakes and misunderstandings relating to class designations of fittings, valves, etc. As an example, few days ago I had a discussion with another engineer because he said: "valves don't have class, so doesn´t matter if we change a valve from class 150 to 300, it only applies to flanges"... After a while and many books and ASME standars open over the table, he finally understood that valves have class like fittings and flanges.
David.